You can leave a 7 year old home alone for 20 minutes as long as the 7 year old is mature enough and has no developmental disabilities or severe autism.
Although, while you can often leave a 7 year old home alone for 20 minutes, pediatricians and even child safety groups state that 7 is too young to be left home alone even for 20 minutes.
Although some 7 year old children can be safely left at home for 20 minutes and others should not as it all depends on your individual 7 year old.
My parents used to leave me alone for around 20 to 30 minutes after school sometimes when they couldn't get home in time and I was fine.
But it can vary from child to child.
Also it's recommended that children shouldn't be left alone at home until they are at least 12 years old.
And at 7 years old, most children lack the quick thinking, impulse control as well as response to crisis that is needed during injuries, fire or an unexpected visitor.
And child welfare laws also focus on whether a child is safe.
And if a 7 year old child does happen to get hurt when being left alone, authorities can still charge you as a parent with child endangerment or neglect.
So if you do need to leave your 7 year old home alone for 20 minutes, if possible let a trusted neighbor know to check on them.